In order to increase the backward momentum and thus make possible an increase in the weight of the ammunition part without excessively high pressure being created behind the weapon, it has been known for many years to introduce what is known as a countermass. When the countermass leaves the rear part of the barrel, it expands and disintegrates. A liquid cloud is formed, which is braked rapidly and produces a pressure-reducing effect adjacent to the weapon. In this connection, reference may be made to our SE patent 8205956-9 which shows an example of a weapon with countermass.
A critical stage in weapons with countermass is the opening phase of the countermass container. In this regard, it is important to obtain symmetrical opening of the cover of the countermass container where all break indications contribute simultaneously to the opening operation. If any part of the cover does not open at the same time as the other parts, an asymmetrical flow is created in the countermass container, which can produce great shear forces on the barrel and also great recoil variations within the temperature range. It may also happen that pieces come away from the cover. Pieces which come away from the cover constitute a great risk behind the weapon.
The opening operation of the cover also depends on the temperature of the weapon or of the countermass container, which can vary between −40° and +60°. In order for the opening operation of the cover to have as small a variation spread as possible and to create optimum opportunities for small recoil spreads, it is important to compensate for pressure variations.
For the functioning of the weapon, it is also important that the countermass has a homogeneous form when it leaves the countermass container.